I too would trim the
acro before moving the clam, but with that said, it can be done. I've moved crocea many times when changing tanks.
If you find the most exposed area at the bottom of the clam, you should be able to use an exacto knife and cut a few byssal threads. DO NOT GO TOO FAST. As you cut a couple, you should be able to "rock" the clam a little more, back and forth (Very gently...do NOT force the clam or you will tear it's gland), exposing more threads. Cut CLOSER to the substrate/rock than the clam itself. You do not want to accidentially knick or sever the byssus gland/port.
While you have the clam off, give it a once over and check for nusiance algae, aptasia, boring sponges etc. When you put it where you want it, use smallish chunks of rubble or
LR to hold it in an area for a couple/few days. If the clam is healthy, it will create a mucous at the port and begin threading itself to the rock again.
Your lighting is such that you could have that clam anywhere in the tank. Unless the tank is unusually tall, you could even put a clam on a flat rock, and settle that on the sand. I'd not worry about adjusting your existing light. That will only throw off the other inhabitants of your system.
Dave
